Slow response in redundant arrays of inexpensive disks

• US 6,321,345 B1
• Filed: 03/01/1999
• Issued: 11/20/2001
• Est. Priority Date: 03/01/1999
• Status: Expired due to Term

• Current Assignee: SeaChange International Incorporated
• Original Assignee: SeaChange Systems, Inc.
• Inventors: Mann, Bruce E., Ywoskus, John A., Trasatti, Philip J.
• Primary Examiner(s): Wright, Norman M.
• Assistant Examiner(s): Revak, Christopher A.
• Application Number:
  US09/260,262
• Time in Patent Office: 995 Days
• Field of Search: 714/5, 714/6, 714/7, 714/8, 714/47, 714/48, 714/55, 714/798, 714/814, 714/815, 713/500, 713/502, 711/112, 711/114, 709/100
• US Class Current: 714/6.22
• CPC Class Codes: G06F 11/1076 Parity data used in redundant arrays of independent storages, e.g. in RAID systems
• CPC Class Codes: G06F 11/1088 Reconstruction on already foreseen single or plurality of spare disks

Abstract

A redundant array includes a plurality of disks, a bus coupling the disks, a receiving device, and a device to reconstruct a block stored in one of the disks. The device reconstructs the block with associated data and parity blocks from other disks. The device transmits the reconstructed block to the receiving device in response to the one of the disks being slowly responding. A method includes requesting a first disk to transmit a first block, reconstructing, when necessary, the first block from associated data stored in other disks of a RAID configuration, and transmitting the reconstructed block directly to a receiving device. The transmitting is in response to the first disk not transmitting the block in a predetermined time.

Claims

1. A redundant array of inexpensive disks comprising:

a pluarality of disks;

a bus coupled to said disks and adapted to transmit data blocks from said disks to a receiving device; and

a reconstructor adapted to reconstruct a data block of one of said disks with associated data and parity blocks from other of the disks and to directly transmit the reconstructed block to the receiving device in response to determining that the one of the disks has not responded within a normal time interval for responding to a read request.

2. The redundant array of claim 1 wherein a slowly responding disk does not complete transmission of a requested data block within a predetermined time.

3. The redundant array of claim 2, further comprising:

a processor adapted to send a signal to the reconstructor in response to the one of the disks slowly responding; and

wherein the reconstructor is adapted to transmit the reconstructed block to the receiving device in response to receiving the signal.

4. The redundant array of claim 3, wherein the processor is adapted to request the other of the disks to send associated data and parity blocks to the reconstructor in response to the one of the disks responding slowly.

5. The redundant data array of claim 3, wherein the processor couples to the plurality of disks and is adapted to control writes of associated data and parity blocks to said disks.

6. A method of transmitting data from a redundant array of inexpensive disks (RAID configuration), comprising:

requesting a first disk of the RAID configuration to transmit a first data block stored therein to a receiving device;

reconstructing the first data block from the associated data stored in other disks of the RAID configuration; and

transmitting the reconstructed first data block directly to the receiving device; and

wherein the reconstructing and the transmitting are performed in response to the first disk providing data in the first data block, but not completing a transmission of the first data block within a normal time interval for responding to a read request.

7. The method of claim 6, wherein the associated data comprises at least one data block and a parity block.

8. The method of claim 6, wherein the reconstructing and the transmitting are performed in response to determining that the first disk is slowly responding.

9. The method of claim 6, further comprising:

providing a time signal at a predetermined time after the requesting; and

wherein the transmitting is in response to an occurrence of the time signal before the first disk completes transmission of the first data block.

10. The method of claim 7, wherein the reconstructing comprises calculating a bit-by-bit exclusive-OR for corresponding bits of data and parity blocks associated with the first data block.

11. A redundant array of inexpensive disks (RAID) configuration to transmit data blocks to a receiving device, comprising:

a plurality of disks adapted to store the blocks and to directly transmit the stored blocks to the receiving device;

a processor to control reads from and writes to the plurality of disks and to determine if one of the disks is responding within a normal time interval; and

a device adapted to reconstruct a block stored in a slowly responding one of the disks from associated blocks stored in others of the disks in response to the processor determining that the one of the disks has not responded within the normal time interval and to directly transmit the reconstructed block to the receiving device.

12. The RAID of claim 11, wherein the processor is configured to determine that the one of the disks is slowly responding if the one disk does not finish transmitting a requested data block within a predetermined time.

13. The RAID configuration of claim 12, further comprising:

a timer coupled to the processor and adapted to count the predetermined time in response to the processor sending a request to a disk to transmit a data block.

14. A two-level redundant array of inexpensive disks (RAID), comprising:

a plurality of second level redundant arrays of inexpensive disks,

a first level processor adapted to write first level blocks to and read first level blocks from the second level arrays; and

each second level array comprising;

a plurality of disks adapted to store second level blocks and to retrieve stored blocks and

a first level device to reconstruct a particuilar first level block from associated first level blocks and to directly transimit the reconstructed first level block to a receiving device in response to a determination that a second level array responding slowly has not responded within a normal time interval.

15. The RAID configuration of claim 14, wherein the first level processor is adapted to signal the first level device that one of the second level arrays is responding slowly if the one of the second level arrays does not complete a transmission of a requested first level block in a predetermined time.

16. The RAID configuration of claim 14, each second level array further comprising:

a second level processor to request reads of and writes to the disks of the associated second level array.